Automobile engine fuel injection control systems which determine the proper air-fuel ratio and constantly monitor the exhaust gas to verify the accuracy of the air-fuel ratio mixture setting are known. Typically, such fuel injection control systems have a facility for intentionally increasing fuel delivery. The intentionally increased fuel delivery is typically effected, when an engine operating condition has fallen into a specific zone of high power engine demand or high engine load, so as to intentionally increase the amount of fuel delivered to the engine and provide the desired, or sufficiently, high engine output power. One such fuel injection control systems is disclosed, for example, in Japanese Unexamined Patent Publication No. 53 - 8427.
In the fuel injection control system described in the above publication, if the engine quickly changes its operating condition into another zone in which engine loads are still high but lower than in the specific zone, and engine speeds are moderated, from the specific zone, the intentionally increased fuel delivery is temporarily suspended. However, the fuel injection control system, if the engine continues to operate in said another zone for a certain period of time, allows the intentionally increased fuel delivery to be re-instated after the lapse of the certain time period. Such a feature of the fuel injection control system is referred to as delayed fuel increase control.
The fuel injection control system, if used for an engine equipped with an automatic transmission, is required in order for the engine to provide the same engine output power as an engine equipped with a manual transmission, to force the engine to operate at a speed higher than the speed at which the engine with the manual transmission operates to provide the same engine output power. This is because the automatic transmission, particularly the torque converter, allows some slippage, thereby sacrificing some of the torque transmitted from the engine. For this reason, the fuel injection control system, when the engine load is increased forces the engine to change its speed directly to one falling in the specific zone for intentionally increased fuel delivery (hereinafter referred to the fuel increase control zone) without transitionally falling into the other zone for delayed fuel increase control (which is hereinafter referred to as the delayed fuel increase control zone). Accordingly, the fuel injection control system, even when the engine operating condition changes to one falling in the delayed fuel increasing control zone, immediately after having been retained in the fuel increase control zone, unavoidably makes an increase in the fuel amount for a short time period while the engine operates at an operating condition in the fuel increase control zone, as to deliver or provide the engine with excess fuel. Particularly, during a kick down condition when fully depressing an accelerator pedal as to open the throttle valve to near its full-open position, the engine is delivered with a considerably excessive amount of fuel.